This invention relates to an apparatus for sealing centrifuge tubes and, more particularly, to an apparatus for sealing centrifuge tubes mounted in rotor cavities.
There is described in the said Romanauskas et. al. patent a seal for a vertically oriented centrifuge tube. Vertically oriented tubes are particularly useful in density gradient separations in which a density gradient in the tube is reoriented from vertical to horizontal during centrifugation and back to vertical for fractionation.
Centrifuge tube caps used prior to those devised by Romanauskas typically were constructed of three parts and were not satisfactory for use with vertically oriented tubes. The parts were not only difficult to assemble and use but also if one wishes to obtain the requisite sealing, a vise was required to hold the closure while being tightened.
The tube cap described by Romanauskas is one in which a tapered plug is introduced into a centrifuge tube disposed in a rotor cavity having a flared mouth. The plug is forced down by a threaded disc which bears axially against the plug so as to wedge the wall of the tube between the plug and the flared mouth of the rotor cavity. Because of the flexibility or resiliency of the tube, a relatively strong, leak proof seal is provided that is effective even under the large pressure forces which occur during centrifugation using vertically oriented tubes. While these seals perform quite satisfactorily, as the diameter of the tubes increase, leakage can sometimes occur, particularly with larger diameter tubes, i.e., those exceeding two centimeters and more. The leakage problem increases as a function of the diameter of the tube, rotor speed and attitude of the tube, i.e., as the tube approaches the vertical or is parallel to the rotational axis, the pressures exerted on the tube cap increase appreciably.
The use of the tapered sealing plugs of this type, while quite satisfactory can cause a problem in that when the plug is pressed downward to seal a particular tube it acts somewhat like a piston. Any air that is above the liquid, if the tube is not completely filled, is compressed. Upon completion of the centrifuge run when the threaded disc or cap, which holds the plug in position, is removed the plug is forced upwardly by the compressed air. Simultaneously with this upward movement, droplets from the liquid within the tube often are expelled because of pressure of the compressed air. Normally this causes no problem. However, if the liquid is biologically dangerous or radioactive, the possibility exists that the rotor may be contaminated. Furthermore, in the centrifugation of light materials, such as lippo proteins, a portion of the sample itself may be lost.
The need exists, therefore, for a relatively easy to use, reliable cap or closure for centrifuge tubes in which the plug and tube are mechanically locked together and sealed against leakage. This permits the tube to be removed in toto from the rotor following centrifugation. The tube may be then placed on a lab bench prior to removing the plug from the tube such that contamination of the rotor is averted.
Another tube cap is described in U.S. Pat. No. 3,938,735 as having a plug portion with inwardly slanting shoulders. Grooves are formed on the shoulders to provide a more effective seal by causing the tube walls to cold flow into the grooves when the tube is sealed. Unfortunately, the plug described is somewhat difficult to remove and is not suitable for use with vertical tube rotors.
It is therefore an object of this invention to provide an improved seal for a centrifuge tube.
A further object of this invention is to provide an improved seal for vertically oriented centrifuge tubes.
In accordance with this invention, a centrifuge rotor for centrifuging a flexible sample container having an open end is constructed to have a rotational axis and a radially spaced, elongated enclosure cavity, with an open end and a longitudinal axis generally parallel to the rotational axis, adapted to receive the container. The open cavity end is flared. A first tapered plug and a retainer secured to the cavity end cooperate to wedge the walls of the open end of the container between the plug taper and the flare. The plug is formed with a peripheral groove in its tapered portion such that when the rotor is operated, the combined forces of the retainer and the hydrostatic forces of the fluid cause the sample container wall to cold flow into the groove forming a sealing and locking ring for the container. This has a particular advantage in that following centrifugation the tube may be removed from the rotor simply by lifting the plug. The plug may then be removed as desired, in some cases by simply depressing the walls of the tubes slightly to distort the ring and disengage it from the groove. The groove may be wedge-like in cross-section; alternatively, it may be round or rectangular in cross-section.